Most refrigeration compressors use mineral oil lubricants with chlorofluorocarbon (CFC) and hydrochlorofluorocarbon (HCFC) refrigerants. In addition to being inexpensive and rugged lubricants, mineral oils are miscible with CFCs and HCFCs, which is important in providing good oil return. In a system with poor oil return, the oil that leaves the compressor collects at various points in the refrigeration system and does not return to the compressor, leading to clogging, poor lubrication, and decreased efficiency.
With continued regulatory pressure limiting the use of ozone depleting substances, the refrigeration industry has been moving to non-ozone depleting hydrofluorocarbon (HFC) based refrigerants. Most HFCs, however, lack the miscibility with traditional lubricants such as mineral oils necessary to provide adequate performance. This has resulted in the implementation of oxygenated lubricants such as polyol ester (POE) oils, polyalkylene glycol (PAG) oils, and polyvinyl ether (PVE) oils or the use of surfactants/solubilizing agents with mineral oils. These new lubricants can be considerably more expensive than traditional mineral oil lubricants and can be extremely hygroscopic. Their combination with water can result in the undesirable formation of acids that can corrode parts of the refrigeration system and lead to the formation of sludges. Consequently, there is a need and opportunity to resolve this low solubility and oil return problem so that the refrigeration industry may utilize halogenated alkene heat transfer agents with hydrocarbon lubricating oils, such as mineral oil and/or alkyl benzene oil, alone or in combination with minor amounts of oxygenated lubricants.
Several refrigerant compositions have been developed incorporating a small fraction of low boiling hydrocarbons, such as butanes or pentanes, for the purposes of improving miscibility with mineral oil and thereby improving oil return. However, it has been recognized that the quantity of hydrocarbon in the refrigerant composition must be minimized to reduce the flammability of the refrigerant composition for the interest of safety, such as taught in U.S. Pat. No. 6,655,160 and U.S. Pat. No. 5,688,432. In the present invention, refrigeration compositions were discovered that provide for acceptable oil return while reducing the flammability risks associated with the hydrocarbon refrigerants.
U.S. Pat. No. 6,516,837 discloses the use of surfactants and/or solubilizing agents with Environmentally desirable refrigerants in systems where chlorine containing refrigerants are being replaced with non-chlorine containing refrigerants. The patent discloses that the surfactants/solubilizing agents are needed because many non-chlorine-containing refrigerants, including HFC's, are relatively insoluble and/or immiscible in the types of lubricants traditionally used such as mineral oil and alkylbenzenes or polyolefins.
WO 2007/002625 discloses the use of various tetrafluoropropenes in a variety of applications including heat transfer systems. The use of lubricants, optionally with compatibilizer to aid compatibility and/or solubility of the lubricant is disclosed. The use of the various tetrafluoropropenes with lubricants such as mineral oils, polyalkylbenzene, polyalkylene glycol oils, and the like is disclosed.
U.S. Pat. No. 5,710,352 discloses methods of preparing 1,1,1,3,3-pentafluoropropane 1-chloro-3,3,3-trifluoropropene and their use as solvents, foam blowing agents, refrigerants, cleaning agents, aerosol propellants, heat transfer media, dielectrics, fire extinguishing compositions and power cycle working fluids.
WO 2006/094303 discloses numerous refrigerant compositions comprising various combinations of selected hydrofluoroolefins, which includes 3,3,3-trifluoropropene, 2,3,3,3-tetrafluoropropene, and 1,3,3,3-tetrafluoropropene, with other hydrofluoroolefins, selected hydrofluorocarbons, selected hydrocarbons, dimethyl ether, carbon dioxide, CF3I, and CF3SCF3. The application further discloses the combination of the refrigerant compositions with lubricating oils including polyol esters, polyalkylene glycols, polyvinyl ethers, mineral oils, alkyl benzenes, synthetic paraffins, synthetic naphthenes, poly(alpha)olefins. The application discloses that the described refrigerants are miscible with lubricants designed for hydrofluorocarbon refrigerants such as polyol esters, polyalkylene glycols, and polyvinyl ethers.
The use of oils other than mineral oil or alkyl benzene oil with more environmentally friendly refrigerants results in increased cost, both due to the higher costs of the oxygenated oils and due problems that arise due to incompatibility in existing equipment that contains mineral oil. The present invention addresses these needs of the refrigeration industry through the discovery of specific halogenated alkene heat transfer fluids which are more miscible with hydrocarbon lubricating oils thereby improving flow and permitting improved lubricant oil transport through a heat transfer system and lubricant oil return back to the system compressor from other system zones without the need for surfactants/solubilizers or oxygenated oils.